Mechanoluminescence and Aggregation-Induced Emission in Bipolar Phenanthroimidazoles: Role of Positional Isomerization-Induced Switching Effect

Abstract

The newborn materials integrated with aggregation-induced emission (AIE) fluorophores, namely PyNPPI-CCz, PyCNPPI-CCz, PyNPPI-NCz, and PyCNPPI-NCz, show intense fluorescence in solution and films. They have good thermal stability (T g /T d , °C: 143/463-PyNPPI-CCz, 156/489-PyCNPPI-CCz, 199/498-PyNPPI-NCz, and 201/501-PyCNPPI-NCz) and exhibit reversible mechanochromism. In the aggregated phase, the restricted intramolecular rotation of phenyl rings reduced the nonradiative relaxation (k nr ) which enhanced the emission intensity with high photoluminescence quantum yield in films (PLQY f ) (0.43-PyNPPI-CCz, 0.68-PyCNPPI-CCz, 0.70-PyNPPI-NCz, and 0.86-PyCNPPI-NCz). The solid state of these materials shows a bluish green emission after grinding, and the color changes are reversible by heating. The reversible mechanofluorochromism can be confirmed by powder X-ray diffraction which implies the transformation between crystalline and amorphous states. Theoretical calculations of molecular couples of these materials suggest that the intermolecular interactions enhanced the dipole moment and the interchange of group positions in these molecules holds much larger dipole moment and contributed to their exceptional mechanoluminance performances.

Stimuli-responsive luminescence from polar cyano/isocyano-derived luminophores via structural tailoring and self-assembly

“…As same as most reports, powder X-ray diffraction (PXRD) revealed that the MCL (Δ λ max = 64 nm) could be attributed to the morphological transformation of these compounds from crystalline to amorphous states. 42 Subsequently, this group replaced the carbazole unit with TPEs, and the new compounds showed variable emission colors by varying water fractions which can be ascribed to the size effect of different aggregates. 43 Moreover, the position effect represented a great influence on the molecular conformation and stacking fashion in different solid states.…”